The present invention pertains to a novel method, technique, and system for coating aircraft fabrics characterized in part by a substantial reduction in the number of coats and in the time involved in the coating process, (and resulting in a finished composition of improved durability and integrity.)
By way of background, it is pointed out that the air frams, e.g. wings and fuslage of light aircraft are, as has been the practice for many years, conventionally covered with cloth, this being done because of the low cost and ease of fabrication and repair involved. In the early days, special grades of cotton were used; after covering the wings or fuselage with such cloth, the cloth was coated by means of multiple applications of nitrocellulose dope. The nitrocellulose dope used was a solution of a high viscosity, high molecular weight nitrocellulose in organic solvents to provide enough strength and shrinking power to tauten the cloth. The concentration of the nitrocellulose in the dope was usually not more than 10% by weight, beacause of the high viscosity that such nitrocellulose imparted to its solutions. Because of such low concentration, five to eight coats of clear dope, followed by two coats of aluminized dope, and three or more coats of pigmented dope were required in oreder to achieve a sufficient buildup. This technique was not only expensive and time-consuming, but dangerous as well, because of the high flammability of nitrocellulose. While lower flammability was later achieved by substitution of cellulose acetate butyrate for the nitrocellulose, it was still necessary to use an undesirably high number of applications to get the necessary buildup.
In more recent times, the use of cotton fabric for air frame covering has been replaced to a significant extent by the use of smooth filament, heatshrinkable polyester fabric of the type commonly termed Dacron, a product of the DuPont Company of Wilmington, Del.
After application of the fabric to an airframe or part thereof, the fabric is tautened by application of heat. While this type of fabric is superior to cotton in its resistance to weathering and to biological or chemical attack, it is difficult to obtain good adhesion of finishing coats thereto, when nitrocellulose or acetate butyrate dope is used as the prime and finishing coats, and such coats have tended to pull away from the fabric substrate rather readily.